This invention relates generally to organophilic clays (hereinafter referred to as xe2x80x9corganoclaysxe2x80x9d), and more specifically relates to organoclays prepared from smectite clays which have been treated with a quaternary ammonium compound of a type commonly referred to as an ester quat. Such ester quats are derived from alkanolamine compounds whose hydroxyl groups are at least partially esterified with carboxylic acids to form a molecule with significant oleophilic properties. The resultant organoclays are useful as functional additives for organic based systems, where they may confer desired mechanical or physical properties sought for such systems.
Organoclays represent the reaction product of a smectite-type clay with a higher alkyl containing ammonium compound (often a quaternary), and have long been known for use in gelling of organic liquids such as lubricating oils, linseed oil, toluene and the like and for use as theological additives in a variety of organic based liquid systems and solvents. The general procedures and chemical reactions pursuant to which these organoclays are prepared are well known. Thus under appropriate conditions the organic compound which contains a cation will react by ion exchange with clays which contain a negative layer lattice and exchangeable cations to form the organoclay products. If the organic cation contains at least one alkyl group containing at least ten carbon atoms then the resultant organoclays will have the property of swelling in certain organic liquids. Among the further prior art patents, which discuss at length aspects of the preparation and properties of organoclays are U.S. Pat. Nos. 2,531,427; 2,966,506; 3,974,125; 3,537,994; and 4,081,496.
As utilized in the present specification, the term xe2x80x9csmectitexe2x80x9d or xe2x80x9csmectite-type claysxe2x80x9d refers to the general class of clay minerals with expanding crystal lattices, with the exception of vermiculite. This includes the dioctahedral smectites which consist of montmorillonite, beidellite, and nontronite, and the trioctahedral smectites, which include saponite, hectorite, and sauconite. Also encompassed are smectite-clays prepared synthetically, e.g. by hydrothermal processes as disclosed in U.S. Pat. Nos. 3,252,757; 3,586,468; 3,666,407; 3,671,190; 3,844,978; 3,844,979; 3,852,405; and 3,855,147.
In addition to their function as thixotropes, organoclays find numerous other applications. Of particular interest for present purposes are composite materials composed of an organic polymer and a smectite-type clay mineral, with the mineral being coupled to the polymer through ionic or other bonding. Prior art pertinent to such composites include U.S. Pat. No. 2,531,3963, published Nov. 28, 1950, wherein a reinforced elastomer is disclosed. Smectite clays such as bentonite and hectorite are base exchanged with organic amines or salts thereof such as triethanolamine hydrochloride. Quaternary ammonium compounds can also be used. The resulting compounds, which are therefore xe2x80x9corganoclaysxe2x80x9d, are added to the lattices of elastomers. The organoclays can be added to the latex of any elastomer including natural rubber, and a large list of polymers and/or copolymers is provided. The resulting compositions can be vulcanized.
Japan Laid Open Application S51(76)-109998, deriving from application SHO 50(1975)-3580 was published Sept. 29, 1976, and is entitled xe2x80x9cMethod for Manufacturing a Clay-Polyamide Compositexe2x80x9d. It discloses a method for manufacturing a clay-polyamide composite characterized by carrying out the polymerization of lactam in the presence of an organoclay made by carrying out ion exchange to bond an organic compound which contains at least one amino group and has the catalyst effect of polymerizing the lactam and clay. The organic compounds mentioned include omega-aminocapronic acid, a nylon salt, hexamethylenediamine, and aminodecanoic acid. The lactams include epsiloncaprolactam and others such as omega-enantolactam, omega-capryllactam, and omegalaurolactam. The clays used include the montmorillonite group of clay minerals such as montmorillonite, hectorite, etc; and other clays are listed. Montmorillonite is preferred because of the high exchange capacity. The composite is made by first ion exchanging the clay with the organic compound under aqueous conditions, after which the which the suspension is washed, filtered and dried, then crushed. (This is essentially the conventional procedure for preparing an organoclay.) The xe2x80x9corganoclayxe2x80x9d and lactam are mixed, with the organoclay being 10 to 75 wt % of the mixture. During mixing the mixture is brought to 80-100 deg C. to melt the lactam. Polymerization is carried out at 240 to 260 deg C. In the resulting composite product it is stated that the silicate layer has a thickness of 9.6 Angstroms. In a first example the interlayer distance of the organoclay layers before polymerization was 3.4 Angstroms, and 13.1 Angstroms after 10 polymerization. In Example 4 the interlayer distance was 6.5 Angstroms before polymerization, and 50.6 Angstroms after polymerization. The composite produced is stated to have good fire-retardant properties, and improved mechanical properties.
Similarly, in Kawasumi et al., U.S. Pat. No. 4,810,734 a process is disclosed wherein a smectite-type clay mineral is contacted with a swelling agent in the presence of a dispersion medium thereby forming a complex. The complex containing the dispersion medium is mixed with a monomer, and the monomer is then polymerized. The patent states that the swelling agent acts to expand the interlayer distance of the clay mineral, thereby permitting the clay mineral to take monomers into the interlayer space. The swelling agent is a compound having an onium ion and a functional ion capable of reacting and bonding with a polymer compound. Among the polymers utilizable are Polyamide resins, vinyl polymers, thermosetting resins, polyester resins, polyamide resins and the like. Related disclosures are found in U.S. Pat. Nos. 4,739,007 and 4,889,885.
In recent years the clay-polymer composite materials above discussed have been referred to as xe2x80x9cnanocompositesxe2x80x9d, a term which reflects their property of exhibiting ultrafine phase dimensions, typically in the range 1-100 nm. The number of nanocomposites based on smectite-type clays and linear thermoplastics is growing. Wang and Pinnavaia, e.g., have reported delamination of an organically modified smectite in an epoxy resin by heating an onium ion exchanged form of montmorillonite with epoxy resin to temperatures of 200-300xc2x0 C. Chemistry of Materials, vol. 6, pages 468474 (April, 1994). Similarly, in U.S. Pat. No. 5,554,670 an epoxy-silicate nanocomposite is disclosed which is prepared by dispersing an organically modified smectite-type clay in an epoxy resin together with diglycidyl ether of bisphenol-A (DGEBA), and curing in the presence of either nadic methyl anhydride (NMA), and/or benzyldimethyl amine (BDMA), and/or boron trifluoride monoethylamine (BTFA) at 100-200xc2x0 C. Molecular dispersion of the layered silicate within the crosslinked epoxy matrix is obtained, with smectite layer spacings of 100 xc3x85 or more and good wetting of the silicate surface by the epoxy matrix. Additional recent references evidencing the increasing interest in nanocomposites incorporating organoclays in polymer matrices include U.S. Pat. Nos. 5,164,440; 5,385,776; 5,552,469; and 5,578,672.
Thus in a typical procedure for preparing a nanocomposite, the smectite clay, most commonly a montmorillonite, is treated with an organic ammonium ion to intercalate the organic molecule between the silicate layers of the clay, thereby substantially swelling or expanding the interlayer spacing of the smectite (The reaction product resulting from this treatment may in accordance with the foregoing discussion, be referred to herein as an xe2x80x9corganoclayxe2x80x9d. Thereafter the expanded silicate layers are separated or exfoliated in the presence of or with the assistance of a polymer with which groups on the intercalated organic molecule are compatible. A monomer can also be used which is polymerized after being intermixed with the intercalated clay.
Now in accordance with the present invention, it has unexpectedly been discovered that organoclays based on specific types of ester quataternary ammonium compounds, are remarkably effective for use in preparing nanocomposites. These organoclays comprise the reaction product of a smectite clay and a quaternary ammonium compound (hereinafter simply xe2x80x9cquatxe2x80x9d) which comprises two esterified radicals (hereinafter called a xe2x80x9cdiester quatxe2x80x9d). The diester quat may be present in admixture with further quaternary ammonium compounds having esterified radicals, especially compounds having three esterified radicals (hereinafter xe2x80x9ctriester quatsxe2x80x9d); or compounds having a single esterified radical (hereinafter xe2x80x9cmonoester quatsxe2x80x9d). Where such a mixture of quats is used, the reaction is between the smectite clay and the quat mixture. In an embodiment, the diester quat should be present as greater than 55 wt % of the quaternary mixture; and the triester quat should be less than 25 wt %, with the fatty acids corresponding to the esters in the mixture having a degree of unsaturation such that the iodine value (xe2x80x9cIVxe2x80x9d) is from about 20 to about 90. In an embodiment, the diester quat content is greater than 60 wt %, the triester quat content is less than 20 wt %, and the IV is from about 30 to about 70. In other embodiments, the diester quat content is greater than 62%, the triester quat content is less than 17 wt %, and the IV is from about 40 to about 60. In some embodiments, an IV from about 45 to about 58 may be desired.